In recent years, because of efficient use of air conditioners due to a rise of awareness about environmental pollution and power saving, there has been an increasing need for limiting ventilation inside a room. When ventilation is limited in such a space where ventilation can be limited, the carbon dioxide concentration in the air increases because of carbon dioxide (CO2) contained in, for example, exhalations of human beings. When the carbon dioxide concentration in the air reaches a particular concentration or higher, carbon dioxide may adversely affect a human body. Therefore, a technique for removing carbon dioxide in the air has been developed in order to prevent an increase in the carbon dioxide concentration.
For example, PTL 1 discloses a technique for removing carbon dioxide in the air through adsorption by using an adsorbent to which an amine-based organic substance is caused to adhere. PTL 2 discloses a technique for removing carbonic acid gas in the air through adsorption by using activated carbon.